Many liquid and semi-liquid products are packaged into large containers for storage and distribution to repackagers, commercial users and other users of large quantities of the product. Many of the these products, particularly food products, deteriorate rapidly when exposed to oxygen. Additionally, food products must be protected against possible contamination from bacteria. Therefore, these products are often placed in large (five gallon) bags made of plastic or similar material and having one spout through which the bag is filled and from which the product is dispensed from the bag. These plastic bags are advantageous in that as the product is dispensed from the container, the bag collapses around the remaining material so that no air enters the container. With containers of a fixed shape or internal volume, air must enter the container to fill the volume left in the container as the product is dispensed. This air contains oxygen and frequently carries harmful bacteria. These containers typically have a rigid or semi-rigid plastic spout through which the product passes to enter or leave the container.
Care must be taken in packaging food products into the containers that no bacteria that would create a potential health risk to the consumer of the food product enter the container. To ensure this sterility, the containers are filled using a chamber that maintains a sterile atmosphere around the spout of the container. Typically, a sterile chamber is filled with a sterile gas, with the gas maintained in the chamber at a positive pressure with respect to the outside environment. The positive pressure of the gas ensures that no air from outside the chamber enters the chamber, as the flow through any opening in the chamber walls is from the higher pressure interior to the lower pressure exterior. A filling head is provided inside the chamber for filling the container with the product. An opening is then provided in the bottom of this chamber that is just large enough to receive the spout of one of the plastic bag food containers. Once the spout is placed in the opening, it is brought into contact with the filling head and the product is dispensed into the bag.
Because of the positive pressure maintained in the chamber, a substantial amount of the gas escapes through the opening, particularly between filling operations after the spout of one container has been removed from the opening and before another has replaced it. Additionally, since the opening must be slightly larger than the spout of the containers, when the spout is in the opening, the gap between the spout and the rim of the opening permits the gas inside the chamber to escape to te outside environment. Because such a large amount of the sterile gas is lost in this way, a number of problems have existed. One of these problems is that only a relatively inexpensive gas can be practically used in the chamber. This has effectively limited the choice of gases to just one gas: hot sterile air. However, use of sterile air, which contains oxygen, exposes the food product to oxygen during the filling operation, which reduces the shelf life of the food product. Also, since the sterile gas must be kept hot to ensure continued sterility of the chamber, large volumes of the gas must be heated. This heating consumes a large amount of energy and requires the use of a considerable amount of equipment.
Thus, a need has existed for an apparatus for filling food containers that uses only a small amount of sterile gas, so that an inert gas could be used as the sterile gas to increase the shelf life of the product being packaged, and so that the heating requirements for the gas could be substantially reduced.